Abstract:

A data storage master disk and method of making a data storage master
disk. The data storage disk master is for use in a data storage disk
replication process. The data storage disk molding processes produces
replica disks having a surface relief pattern with replica lands and
replica grooves. The method includes providing a master substrate. The
master substrate is at least partially covered with a layer of
photosensitive material. A surface relief pattern having master lands and
master grooves is recorded in the data storage disk master, including the
steps of exposing and developing the photosensitive material is
controlled to form master grooves extending down to a substrate interface
between the master substrate and the layer of photosensitive material,
such that the width of the master grooves at the substrate interface
corresponds to a desired width of the replica lands.

Claims:

1-49. (canceled)

50. A replica disk comprising:a replica substrate including a first major
surface and a second major surface, the first major surface including a
surface pattern defined by lands and interrupted grooves,wherein the
surface pattern defines a track pitch that is less than 425
nanometers,wherein tops of the lands define widths between 25 percent of
the track pitch and 140 nanometers, andwherein the grooves define depths
between 20 and 120 nanometers.

51. The replica disk of claim 50, wherein the widths of the tops of the
lands are greater than 35 percent of the track pitch.

52. The replica disk of claim 50, wherein the tops of the lands are
substantially flat and coplanar.

53. The replica disk of claim 52, wherein the widths of the tops of the
lands are greater than 35 percent of the track pitch.

54. The replica disk of claim 50, wherein the depths of the grooves are
between 55 and 110 nanometers.

55. The replica disk of claim 54, wherein the tops of the lands are
substantially flat and coplanar.

56. The replica disk of claim 54, wherein the widths of the tops of the
lands arc greater than 35 percent of the track pitch.

57. The replica disk of claim 56, wherein the tops of the lands are
substantially flat and coplanar.

Description:

[0001]This application is a continuation of U.S. application Ser. No.
10/790,965, filed Mar. 2, 2004, which is a continuation of U.S.
application Ser. No. 09/850,252, filed May 7, 2001, which is a divisional
application of U.S. application No. 09/730,246, filed Dec. 5, 2000, which
is a continuation-in-part (CIP) of U.S. application Ser. No. 09/055,825,
filed Apr. 6, 1998, now abandoned. The entire content of each of the
aforementioned applications is incorporated herein by reference.

TECHNICAL FIELD

[0002]The present invention relates generally to the field of manufacture
of optical data storage disks, and in particular, to an optical disk
mastering process for use in a disk molding process, capable of molding
data storage disks containing a high density of information.

BACKGROUND OF THE INVENTION

[0003]Optical disks are produced by making a master which has a desired
surface relief pattern formed therein. The surface relief pattern is
created using an exposure step (e.g., by laser recording) and a
subsequent development step. The master is used to make a stamper, which
in turn is used to stamp out replicas in the form of optical master
substrates. As such, the surface relief pattern, information and
precision of a single master can be transferred into many inexpensive
replica optical disk substrates.

[0004]During the mastering exposure step, the mastering system
synchronizes the translation position of a finely focused optical spot
with the rotation of the master substrate to describe a generally
concentric or spiral pattern of a desired track spacing or "track pitch"
on the disk. The generally spiral track forming the desired surface
relief pattern as a result of the mastering process can be defined by
high regions termed "lands" and lower adjacent regions termed "grooves"
and/or pits (i.e., interrupted grooves). The recording power and
size/shape of the focused optical spot (spot size) as well as the
photosensitive material parameters determine the final geometry revealed
in the master disk during the subsequent development step. Normal
mastering practice uses high contrast positive photoresist for the
photosensitive material.

[0005]Conventional mastering typically utilizes laser light with
wavelength, λ, in a range of 350 nm<λ<460 nm focused
through an objective with a numerical aperture (NA) of 0.75
nm<NA<0.90 to give a theoretical Gaussian spot size of:

[0006]After the master is recorded, it is flooded with developer solution
to reveal the exposure pattern applied by the master recording system.
The dissolution of the photoresist in the developer solution is in
proportion to the optical exposure previously received in the recording
process. The dissolution rate of the photoresist can be modeled for given
exposure and development conditions (see Trefonus, P., Daniels, B., "New
Principal For Imaging Enhancement In Single Layer Positive Photoresist,"
Proc. of SPIE vol. 771 p. 194 (1987), see also Dill F. et al.,
"Characterization of Positive Photoresists" IEEE Transactions on
Electronic Devices, vol. ED-22 p. 445 (1975).) Expressions explained in
these referenced technical papers can be used to model the effects of
exposures from several adjacent tracks recorded in the photoresist and
subsequently developed. The photoresist dissolution in the developer
solution is in proportion to the optical exposure previously received
(positive type resist). More accurately, the dissolution rate (R) is
given by the Trefonas model as

R [nm/sec]=R0x(1-M)1+Rb

Where R0 and Rb are the dissolution rates of the fully exposed
and unexposed photoresist (respectively), q is a resist parameter related
to the resist contrast and M is the fractional unconverted photoactive
compound in the resist. Typical values for commercially available resists
are q=3, 10<R0<200 [nm/sec] and Rb=0 for normal developer
concentrations. The M term is dependent in a point-wise fashion on how
much exposure was received in the resist (E(x,y,z)) and the resist's
parametric sensitivity "C" per the Dill convention:

M(x,y,z)=exp {-C×E(x,y,z)}.

[0007]Since optical disk mastering typically uses only 50-200 nm of
photoresist thickness, the z-dependence of exposure can safely be ignored
so that the above equations can be combined to give

R=R0(1-exp {-CE(x,y})1;

or, with the exposure profile explicitly circular gaussian we may simplify
to

R=R0(1-exp {-CkP exp [-r2/SS2]})q;

[0008]Where r measures the radial distance from the center of the spot
(r2=x2+y2), P is the recording power and k is a
normalization constant for the guassian function. This dissolution rate,
multiplied by the development time (td), gives the depth of
photoresist lost from its initial coating thickness (T0), so that
the final resist thickness (T(t)) is given by T(td)=T0-td
R0(1-exp {-CkP exp [-r2/SS2})q; From this expression
one can see how optical exposure (P), development (td, R0) and
photoresist thickness (To) determines final surface relief pattern.

[0009]In some aspects, these expose/development processes may be compared
with conventional photography. In photography, either exposure or
development may be controlled/adjusted as necessary to obtain desired
final development pattern. In this sense, one may consider the
expose/development level as one process variable which may alternatively
be controlled by recording power, development time, developer
concentration, etc.

[0010]In the mastering process, it is desirable to simultaneously obtain
wide lands (for user recorded features) and grooves of suitable depth for
adequate tracking signals (e.g., greater than 50 nm). Higher density data
storage disks often require the storage or a greater amount of
information within the same or smaller size of disk area, resulting in
smaller track pitch (i.e., distance between tracks) design criteria.

[0011]Attempts have been made to meet these design criteria. In prior art
FIGS. 1-3, surface relief patterns of exemplary master disks formed using
conventional disk mastering techniques are illustrated using the above
expressions to model the effects of exposures from several adjacent
tracks recorded in the photoresist layer and then developed. These
comparisons assume (1) typical photoresist and developer parameters, (2)
constant development time (=40 sec.), (3) SS=0.23 microns, (4) track
pitch of 0.375 microns and initial photoresist thickness of 100 nm. As
recording power (or alternatively, development time) is increased to
obtain deeper grooves, the residual land width diminishes and lands
become more rounded due to overlap exposure from adjacent tracks.
Partially developed photosensitive material exhibits a granular roughness
greater than that of the photosensitive material as initially coated on
the disk. Roughness of lands worsens with deepening of grooves, resulting
in additional noise in data readback.

[0012]More problems occur when the track pitch approaches the finite size
of the mastering spot size. For formats where the desired track pitch is
much larger (>2×) than the finite size of the mastering spot
size (ss), the photosensitive material erosion of the lands is negligible
and conventional mastering can provide wide lands with a >50 nm groove
depth, or both (due to overlap exposure from adjacent tracks).

[0013]In FIG. 4, exemplary embodiments of the mandatory link between land
width and groove depth when using conventional mastering processes is
illustrated. (Examples of 0.375 micron and 0.425 micron track pitch with
0.22 micron recording spot size). As the groove depth increases, the land
width decreases. The master surface relief pattern geometrics (i.e., land
width/groove depth) are constrained for given conditions of track pitch
and mastering spot size. This means the designer may not independently
specify the desired parameters for replica land width and replica groove
depth.

[0014]A secondary problem for conventional mastering is that the land
width precision is limited by mechanical track pitch precision (e.g.,
mechanical precision of master recording system), which is increasingly
difficult to control as track pitch decreases.

SUMMARY OF THE INVENTION

[0015]The present invention provides a data storage master disk and method
of making a data storage master disk wherein the user may independently
specify the parameters of replica land width and replica groove depth.
The data storage master disk is for use in a data storage disk molding
process for producing replica disks which are capable of storing a high
capacity of information using a variety of disk formats.

[0016]In a first embodiment, the present invention provides a method of
making a data storage master disk for use in a data storage disk molding
process. The data storage disk molding process produces replica disks
having a surface relief pattern with replica lands and replica grooves.
The method includes the step of providing a master substrate. The master
substrate is covered with a layer of photosenstive material having a
specified thickness. A surface relief pattern having master lands and
master grooves is recorded in the data storage master disk, including the
steps of exposing and developing the photosensitive material. The
exposing and developing of a specified thickness of a photosensitive
material is controlled to form master grooves extending down to a
substrate interface between the master substrate and the layer of
photosensitive material, such that the width of the master grooves at the
substrate interface corresponds to a desired width of the replica lands.

[0017]The thickness of the photosensitive material is specified and
controlled to correspond to a desired depth of the replica grooves. In
another aspect, the thickness of the photosensitive material is specified
and controlled in dependence on master recording system spot size,
desired track pitch, and desired depth of replica grooves. The step of
controlling the exposure and development of the data storage master disk
may include the step of controlling the exposing and developing of the
photosensitive material to obtain a flat master groove bottom. In another
aspect, the step of controlling the exposure and development of the data
storage master disk includes the step of controlling the exposing and
developing of the photosensitive material to obtain a smooth, flat master
groove bottom, with smoothness determined by the master substrate.

[0018]The step of controlling the exposing and developing of the
photosensitive material may include the step of controlling optical
energy for exposing the photosensitive material to a degree sufficient to
obtain a desired master groove bottom width after development and removal
of the photosensitive material. In another aspect, the step of
controlling the exposing and developing of the photosensitive material
may include the step of controlling the development of the photosensitive
material to a degree sufficient to obtain a desired master groove width
after development and removal of the exposed photosensitive material.

[0019]The step of exposing and developing the data storage master disk may
include the step of forming a groove bottom, wherein the groove bottom is
flat relative to the master land. The step of exposing and developing the
data storage master disk results in the data storage master disk having a
master surface relief pattern defined by the master lands and the master
grooves, wherein the surface relief pattern of the replica disks has an
orientation which is inverse the orientation of the data storage master
disk surface relief pattern.

[0020]The present invention may further provide the step of polishing the
master substrate optically smooth; and forming a smooth master groove
bottom using the master substrate. In one aspect, the step of providing a
master substrate includes forming a master substrate made of glass.
Preferably, the glass is polished. The photosensitive material may be
bonded to the master substrate with or without intermediate layers.

[0021]The present invention may further provide for forming a first
stamper using the data storage master disk. Replica disks are made using
the first stamper. The step of making replica disks using the data
storage master disk may be accomplished using a multiple generation
stamper process.

[0022]In another embodiment, the present invention provides a method of
making a replica disk from a master disk using an inverse stamping
process. The replica disk is capable of storing high volumes of
information. The replica disk includes a surface relief pattern with
replica lands and replica grooves. The method includes the step of
providing a master substrate. At least a portion of the master substrate
is coated with a layer of photosensitive material to form the master
disk. A surface relief pattern having master lands and master grooves is
recorded in the master disk, including the steps of using a laser beam
recorder for exposing the photosensitive material in a desired track
pattern having a track pitch, and developing the photosensitive material.
The exposing and developing of the photosensitive material is controlled
for forming master grooves extending down to a substrate interface
between the master substrate and the photosensitive material, such that
the width of the master grooves at the substrate interface corresponds to
a desired width of the replica lands. A first stamper is formed from the
master disk. A second stamper is formed from the first stamper. A replica
disk is formed from the second stamper, the replica disk including a
surface relief pattern having an orientation which is the inverse of the
master disk.

[0023]The present invention may further provide the step of controlling
the thickness of the layer of the photosensitive material to correspond
to a desired depth of the replica grooves. The specified and controlled
thickness of the photosensitive material depends on master recording
system spot size, desired track pitch, and desired depth of replica
grooves.

[0024]The step of controlling the exposing and developing of the
photosensitive material may include the step of controlling the exposing
and developing of the photosensitive material to obtain a flat master
groove bottom. Recording a desired track pitch in the photosensitive
material may further include the use of a focused laser beam at a spot
size which is greater than one half of the track pitch.

[0025]The step of a master substrate may include providing a master
substrate made of glass. Further, the master substrate may be polished.

[0026]In one aspect, the desired track pattern is a spiral track defined
by adjacent master lands and master grooves, wherein the steps of
exposing/developing the master disks includes forming a wide, flat master
groove bottom defined by the disk substrate. The step of recording the
master disk includes forming master groove bottoms having a width which
does not necessarily depend on the depth of the master groove for a
desired track pitch. The resulting depth of the master groove is
dependent on the specified thickness of the photosensitive material and
the cumulative optical exposure received by the photosensitive layer at a
position half way between two adjacent tracks. In particular, this
depends on the desired groove bottom width and the ratio of master
recording spot size to desired track pitch.

[0027]In another embodiment, the present invention provides a master disk.
The master disk includes a master substrate. A layer of photosensitive
material covers at least a portion of the master substrate. The
photosensitive material includes a surface relief pattern in the form of
a track pattern defined by adjacent master lands and master grooves. The
master grooves extend down to the disk substrate, the master grooves
including a master groove bottom and the master lands including a master
land top, wherein the master groove bottom is wider than the master land
top.

[0028]The master groove bottom is generally flat. In particular, the
master groove bottom is flat relative to the master land top, and in
particular, the master groove bottoms may be wide and flat relative to
the master land tops. Preferably, the master groove bottoms include sharp
corners. Additionally, all of the master groove bottoms on the
exposed/developed master disk are level with each other to the precision
of the master substrate flatness. This is important in flying head media
applications, such as near field recording techniques, where small lenses
fly in proximity to the replica disk surface.

[0029]The master grooves may include a groove depth which is proximate the
thickness of the photosensitive material for cases where the track pitch
is greater than approximately 1.6 times the spot size. In one aspect, the
master grooves include a groove depth which is greater than 50
nanometers, track pitch is less than two times the mastering system spot
size, and the width of the master groove bottom is greater than 25
percent of desired track pitch. In another aspect, the width of the
master groove bottom is greater than 50 percent desired track pitch.

[0030]In another embodiment, the present invention provides a disk
including a replica substrate having a first major surface and a second
surface. The first major surface includes a surface relief pattern in the
form of a track pattern defined by adjacent lands and grooves. The track
pattern having a track pitch less than 425 nanometers, wherein the
grooves extend down into the disk substrate. The grooves include a groove
bottom and the replica lands include a land top, wherein the land top is
flat. This is particularly important in near field recording techniques,
wherein lens-to-media-surface separation is extremely critical.

[0031]In one aspect, the land top has a width greater than 25 percent of
crack pitch. In one preferred aspect for the track pitch less than or
equal to 400 nanometers, the groove depth is greater than 80 nanometers
and the land width is greater than 160 nanometers. Preferably, the land
top is smooth and has sharp edges. In one preferred embodiment, the land
tops are level with each other to the precision of the flatness of the
master disk substrate. The land tops are level and at the same elevation
relative to the second major surface. This is important in flying head
media applications, such as near field recording techniques, where small
lenses fly in proximity to the replica disk surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]The accompanying drawings are included to provide a further
understanding of the present invention and are incorporated in and
constitute a part of this specification. The drawings illustrate the
embodiments of the present invention and together with the description
serve to explain the principals of the invention. Other embodiments of
the present invention and many of the intended advantages of the present
invention will be readily appreciated as the same become better
understood by reference to the following detailed description when
considered in connection with the accompanying drawings, in which like
reference numerals designate like parts throughout the figures thereof,
and wherein:

[0033]FIG. 1 is a partial cross section illustrating the surface relief
pattern of a prior art recorded master disk;

[0034]FIG. 2 is a partial cross-section illustrating the surface relief
pattern of another master disk made using a prior art recording process;

[0035]FIG. 3 is a partial cross-section illustrating the surface relief
pattern of another master disk made using a prior art recording process;

[0036]FIG. 4 is a graph illustrating master groove depth versus master
land width for a master disk made using prior art mastering/recording
techniques;

[0037]FIG. 5 is a plan view illustrating one exemplary embodiment of a
recorded master disk made using a data storage disk mastering process in
accordance with the present invention;

[0038]FIG. 6 is an enlarged partial cross-sectional view taken along line
6-6 of FIG. 5;

[0039]FIG. 7 is an enlarged partial cross-sectional view illustrating a
step in making a master disk in accordance with the present invention;

[0040]FIG. 8 is a diagram illustrating another step in making a master
disk in accordance with the present invention;

[0041]FIG. 9 is a diagram illustrating one exemplary embodiment of the
surface geometry of a master disk made using the process in accordance
with the present invention;

[0042]FIG. 10 is a diagram illustrating another exemplary embodiment of
the surface geometry of a master disk made using the process in
accordance with the present invention;

[0043]FIG. 11 is a diagram illustrating another exemplary embodiment of
the surface geometry of a master disk made using the process in
accordance with the present invention;

[0044]FIG. 12 is a graph illustrating maximal master groove depth versus
master groove bottom width for examples of master disks made using the
mastering process in accordance with the present invention;

[0045]FIGS. 13-18 illustrate experimental atomic force microscope traces
of several differing surface relief geometries for master disks recorded
at 0.375 and 0.425 micron track pitch using the mastering process in
accordance with the present invention;

[0046]FIG. 19 is a diagram illustrating groove orientation for replica
disks made from a master disk in accordance with the present invention,
using a multiple generation disk molding/replication process;

[0047]FIG. 20 is a block diagram illustrating a data storage disk
mastering process in accordance with the present invention; and

[0048]FIG. 21 is a block diagram illustrating a process for making a
replica disk using a master disk in accordance with the present
invention.

DETAILED DESCRIPTION

[0049]The present invention includes a data storage master disk and
optical disk mastering process for making the unique data storage master
disk. The process in accordance with the present invention provides for a
master data storage disk having grooves which extend down to the master
substrate, resulting in deep, flat, and wide master disk grooves. The
master disk can be used in a disk molding process which includes a
reverse mastering/inverse stamping process, resulting in replica disks
having wide, flat lands with sharp edges, and deep grooves relative to
replica disks formed using conventional mastering processes. As such, the
present invention is particularly useful in enabling flexible design of
surface relief geometry for molded data storage disks containing a high
density of information. This includes the ability to create wide, flat
land features even in replica disks having a track pitch of less than two
times the mastering system laser beam spot size.

[0050]In FIG. 5, a data storage master disk 20 in accordance with the
present invention is generally shown. Master disk 20 may be used as part
of a disk replication process (e.g., a disk molding process) for
producing various formats of optical data disks. The data features on the
optical data disks may include data pits, grooves, bumps or ridges, and
land or land areas. This includes current formats of audio CD, CD-ROM and
video disk, such as DVD, as well as future formats which use data
features described herein. The definition of optical data disks may
include various types of recordable optical disks (e.g., CDR,
magneto-optic, or phase-change disk formats, which commonly use features,
such as grooves or pits, for tracking and address identification, even
though data is subsequently recorded by the users.

[0051]Master disk 20 includes a surface relief pattern (i.e., surface
geometry) in the form of "data tracks" 22 (shown enlarged for clarity)
which may include features representing data encoded therein or which
allow the storage, reading, and tracking of data thereon. Data tracks 22
on the optical disk can be arranged in a spiral track 24 originating at
the disk center 26 and ending at the disk outer edge 28, or
alternatively, the spiral track 24 may originate at the disk outer edge
28 and end at the disk center 26. The data can also lie in a series of
concentric tracks spaced radially from the disk center 26. Master disk 20
may or may not include a center hole, and may be hubbed or hubless.

[0052]In FIG. 6, a partial cross-sectional view illustrating one exemplary
embodiment of master disk 20 in accordance with the present invention is
shown. Master disk 20 includes data layer 30 and master substrate 32 (a
portion of which is shown). The data layer 30 includes a surface relief
pattern shown as data tracks 22. The data tracks 22 are defined by a
series of adjacent master lands 34 and master grooves 36 formed in the
data layer 30 (e.g., which form spiral track 24). The master groove sides
38, 40 are defined by adjacent master lands 34, and include a master
groove bottom 42 which is defined by the master substrate 32. Master
substrate 32 provides for a wide, flat and smooth master groove bottom
42.

[0053]Data layer 30 is made of a photosensitive material, and more
preferably, is made of a photopolymer or photoresist. Master grooves 36
have a depth 44 which is equal to the height of master lands 34 relative
to master substrate 32, and related to the initial thickness of data
layer 30. Master groove depth 44 may further be dependent on mastering
spot size, track pitch, and photoresist contrast. Preferably, master
grooves 36 have a depth greater than 50 nm, and which typically ranges
between 50 nm and 120 nm. Master groove bottom 42 is preferably flat and
smooth as defined by master substrate 32, having a width 46 which is
preferably greater than 35 percent of the desired track pitch.

[0054]In one preferred embodiment, master substrate 32 is made of glass,
and is preferably polished and/or optically smooth. The master substrate
32 typically varies in thickness between 5 mm and 6 mm. Data layer 30 can
be bonded to master substrate 32. In particular, data layer 30 may be
coated directly to master substrate 32 or may include an intermediate
layer (which may be a bonding layer).

[0055]The disk mastering process in accordance with the present invention
provides for master disk 20 having relatively deep master grooves 36 with
wide, flat master groove bottoms 42. As such, when master disk 20 is used
in a reverse optical disk mastering process, the master lands and master
grooves translate into a replica disk having relatively deep grooves and
wide flat lands. Such characteristics are preferred for many high density
and writeable optical disk formats.

[0056]The master groove bottoms defined by the disk mastering process in
accordance with the present invention are flat (as opposed to rounded in
the conventional process) with smoothness defined by the master substrate
(e.g., polished glass) and includes sharp corners. When used in
connection with an inverse stamping process, this corresponds to replica
disks having wide, flat smooth lands with sharp corners, and deep
grooves. Wide, flat lands are advantageous for positioning user recorded
data thereon. The sharp corners provide domain confinement for user
recorded data (e.g., applications wherein data is magneto-optically
recorded on the tops of lands). The wide, flat lands with sharp corners
and deep grooves provide for improved tracking or trackability of the
media substrate. The replica disk land tops are very smooth, due to the
groove bottoms 42 which are defined by the master substrate 32. which is
preferably optically polished glass. The smoothness of the land tops is
defined by the substrate interface between the master substrate 32 and
the layer of photosensitive material 30. Smoothness of land tops results
in a reduction of noise in subsequent readout of data from the disk.

[0057]Further, the wide, flat lands are level with each other, due to the
groove bottoms 42 being defined by the master substrate 32. The flat
lands are level with each other and at the same elevation, enhancing the
flyability of the disk substrate for flying head applications.

[0058]Referring to FIGS. 7 and 8, a method of making an optical disk
master for use in a data storage disk molding process, in accordance with
the present invention, is illustrated. In FIG. 7, master substrate 32 is
provided which is preferably made of glass. Master substrate 32 typically
ranges in thickness between 5 mm and 6 mm. Master substrate 32 includes
major surface 50. Preferably, major surface 50 is polished optically
smooth. Major surface 50 is at least partially covered (e.g., coated) by
data layer 30. Data layer 30 may also be coated over an intermediate
(e.g., bonding) layer 60 (not shown).

[0059]Referring to FIG. 8, master disk 20 is positioned on a master
recording system (e.g., a laser recorder or a mask recording system). In
one exemplary embodiment, the master recording system 60 includes
controller 61, linear translation system 62, master recorder 64, and
recording table 66. Master recording system 60 provides for controlled
exposure of master disk 20 with a focused spot of laser light to encode
the desired surface relief pattern (i.e., geometry) or data tracks
therein.

[0060]Master disk 20 is placed on recording table 66, and can be
registered (e.g., centered) about a center axis 68, relative to master
recorder 64 using techniques as known in the art, such as through the use
of a spindle, or hubbed master disk 20. Recording table 66 is rotatable
about the center axis 68, indicated by rotation arrow 70, for rotation of
master disk 20 during the disk recording process. Master recorder 64
modulates and focuses a laser beam 72 for exposure of data layer 30 in a
desired pattern. Further, master recorder 64 is mechanically coupled to
linear translation system 62 which provides for axial movement of master
recorder 64 relative to center axis 68, indicated by directional arrow
76.

[0061]Controller 61 is coupled to linear translation system 62 and master
recorder 64 (indicated at 61A) and is coupled to recording table 66
(indicated at 61B). The controller 61 operates to synchronize the
translation position of the finally focused laser beam 72 with the
rotation 70 of master disk 20 to expose spiral track 24 in data layer 30.
Further, controller 61 may operate to modulate laser beam 72 to expose
pit regions (interrupted grooves) in the header area of the disk.
Controller 61 can be a microprocessor based programmable logic
controller, a computer, a sequence of logic gates, or other device which
may be capable of performing a sequence of logical operations.

[0062]In accordance with the present invention, controller 61 operates to
control the optical energy of master recording system 60 for exposing the
photosensitive material of master disk 20 to a degree sufficient to
obtain a desired master groove bottom width after development and removal
of the exposed photosensitive material. Controlling the optical energy
can include controlling either the recording power or controlling the
recording speed for exposing the photosensitive material to a degree
sufficient to obtain a desired master groove bottom width after
development and removal of the exposed photosensitive material. For
example, controller 61 may operate to increase the recording power or
decrease the recording speed, thereby increasing optical exposure of the
photosensitive material.

[0063]The laser recorded master disk 20 is removed from the recording
table 66 and flooded with a developer solution to reveal the exposure
pattern provided by the master recording system 60. The amount of
dissolution of the data layer 30 in the developer solution is in
proportion to the optical energy previously received during the recording
process. Further, the amount of dissolution of the data layer 30 in the
developer solution is in proportion to development process parameters,
including the concentration of the development solution, the development
time and temperature. The type of development solution can be similar to
development solutions used in conventional recording processes as known
to those skilled in the art. As such, by controlling the exposure and
development processes, the desired surface relief pattern in the
photosensitive material can be achieved. Since the master recording
system 60 was controlled to fully dissolve portions of the data layer 30
down to the master substrate 32, the resulting master grooves (previously
shown in FIG. 6) include master groove bottoms which are defined by the
master substrate 32 and, in particular, for recorded track pitches of
less than 2 times the mastering spot size. The above master disk process
results in master lands having rounded peaks and master grooves having
flat, wide and preferably smooth master groove bottoms.

[0064]In FIGS. 9-11, exemplary embodiments are shown illustrating the
surface relief pattern or data tracks for master disks 20A, 20B, 20C
which have been "overexposed" or "overdeveloped" using the master
recording process in accordance with the present invention. With each
figure (i.e., FIG. 9-11), the amount of exposure/development of data
layer 30 has been increased. Referring to FIG. 9. the master
recording/developing process resulted in master lands 34A defining master
grooves 36A exposed down to master substrate 32A. Master grooves 36A have
a groove depth of 92 nm with a corresponding flat master groove bottom 42
having a width of 120 nm. Similarly, FIG. 10 illustrates surface relief
pattern or data tracks 22B having master lands 34B which define master
grooves 36B down to master substrate 32B. The master grooves 36B have a
groove depth of 88 nm and a corresponding flat master groove bottom 42
which is 160 nm wide. FIG. 11 illustrates master disk 20C having master
lands 34C which define master grooves 36C having master groove bottom 42C
defined by master substrate 32C. Master groove 36C has a groove depth of
82 nm and a flat groove bottom 42 which is 200 nm wide. The more master
disk 20 is overexposed during disk recording process, the greater the
erosion of the master lands and wider master groove bottoms are achieved.

[0065]In FIG. 12, a graph illustrating the corresponding relationship
between master land width and master groove depth using the master
recording process in accordance with the present invention is shown.
Using conventional mastering processes, for a given data layer thickness,
master groove depth and master groove bottom width are linked and
dependent upon each other (see FIG. 4). Using the mastering process in
accordance with the present invention, by selection of the initial
thickness of the data layer and expose/development level, one can
independently specify land width and groove depth. In other words, master
groove depth is not dependent upon master groove bottom width, and master
groove bottom width is not dependent upon master groove depth. The two
parameters are separable, and by selecting a desired data layer
thickness, and controlling exposure and development criteria, a desired
design criteria for the master disk may be obtained.

[0066]In the exemplary embodiment shown, plots are shown illustrating
design criteria achieved by increasing initial photosensitive (data)
layer thickness (plot 78) and/or increasing exposure energy/development
of the photosensitive layer (plot 79). In all examples, a 0.22 micron
spot size is assumed. Plot 80 had an initial data layer thickness of 120
nm, plot 82 had an initial data layer thickness of 100 nm, plot 84 had an
initial data layer thickness of 80 nm, and plot 86 had an initial data
layer thickness of 60 nm. As illustrated, master surface geometries are
no longer constrained by the master land width to master groove depth
linkage as in conventional mastering processes. By starting with
different initial data layer thicknesses and controlling
expose/development level, any point within the width-depth parameter
space may be obtained using the disk mastering process in accordance with
the present invention. Whereas FIG. 12 shows how by starting with
differing initial photosensitive material thickness that any point in the
width-depth parameter space may be obtained, FIGS. 13-18 show
corroborating experimental results illustrated by atomic force microscope
(AFM) traces of several differing geometries at 0.375 and 0.425 micron
track pitch using the disk mastering process in accordance with the
present invention.

[0067]The mastering recording process in accordance with the present
invention is (preferably) used in a reverse mastering or inverse stamping
process, for creation of replica disks having wide, flat (and smooth)
land features at track pitches less than two times the mastering system
spot size. In FIG. 19, a diagram illustrating "groove" orientation of an
optical disk substrate (i.e., a replica disk) molded from a first
generation stamper, a second generation stamper or a third generation
stamper formed from a master disk in accordance with the present
invention, is shown. The diagram includes enlarged, partial
cross-sections illustrating the orientation of the data tracks of a
master disk 90, first generation stamper 92, second generation stamper
94, third generation stamper 96, replica disk substrate 1, replica disk
substrate 2, and replica disk substrate 3. Data tracks are recorded onto
the master disk 90, and have an orientation based on whether a replica
disk substrate is molded from a first, second or third generation
stamper.

[0071]It is recognized that the desired orientation of the master disk
data layer 104 is dependent on the desired orientation of the replica
disk substrate for its intended use. For the example of high-density
replica disks having track pitches less than two times the mastering
system spot size (and air incident media), it is desirable to use a
master disk form using the master disk recording process in accordance
with the present invention and a second generation stamper process,
resulting in a replica disk having wide, flat, smooth lands and deep
grooves. Alternatively, for disks read through the substrate, a master
disk formed using the master disk recording process in accordance with
the present invention may be used in a first generation stamper or third
generation stamper process where it is desired to mold a replica disk
having flat pits or grooves.

[0072]In one preferred embodiment, a master disk made using the master
disk recording process in accordance with the present invention is
utilized in a second generation disk molding process. Suitable disk
molding processes including one suitable second generation disk molding
process capable of making multiple optical disk stampers from one master
disk is as disclosed in U.S. Pat. No. 6,365,329, the disclosure of which
is incorporated herein by reference. The above-referenced patent utilizes
a unique disk molding process which includes a photopolymerization step
which is non-destructive to either the recorded master, first generation
stamper or second generation stamper. This allows many next generations
stampers to be made, while maintaining the integrity of the data layer
transferred from the previous generation disk. In one embodiment, a
portion of a first stamper which defines the data layer is transferred to
and becomes part of a second stamper without changing the integrity of
the data layer.

[0073]Alternatively, other stamper processes may be utilized. For example,
in another exemplary embodiment an electroforming pyramiding family
process is used. This process involves the electroforming of a "father"
stamper or first generation stamper from a master disk formed using the
process in accordance with the present invention. The father stamper is
cleaned, treated and returned to the nickel bath to plate a "mother" or
second generation stamper. This process cycle can be repeated several
times, resulting in multiple "mother" stampers or second generation
stamper being made from a single father or first generation stamper. The
same electroforming process may be repeated using the "mother" stamper to
make several "daughter" or third generation stampers from each mother.

[0074]In FIG. 20, a block diagram illustrating a process for making a
replica disk using a master disk made in accordance with the present
invention is shown at 110. The master disk is for use in a data storage
disk molding process. The data storage disk molding process produces
replica disks having a surface relief pattern with replica lands and
replica grooves. In the exemplary embodiment shown, the process 110
begins with providing a master substrate (112). The master substrate is
at least partially covered with a photosensitive material, which is
preferably made of photoresist (114). A surface relief pattern having
master lands and master grooves is recorded in the data storage master
disk, including the steps of exposing and developing the photosensitive
material (116). The exposing and developing of a specified thickness of
photosensitive material is controlled to form master grooves extending
down to substrate interface between the master substrate and the layer of
photosensitive material, such that the width of the master grooves at the
substrate interface corresponds to a desired width of the replica lands
(118).

[0075]The master disk can now be used to make a replica disk in a disk
molding process. In particular, a stamper is made from the optical master
disk (120). A replica disk is made from the stamper (122). The replica
disk is capable of storing high volumes of information. In one
application this invention is particularly useful for recording track
pitches that are less than 2 times the master recorder spot size.

[0076]In FIG. 21, a block diagram illustrating one exemplary embodiment of
using a master disk in accordance with the present invention in a
multiple generation disk molding process is shown at 130. The master disk
is fabricated (132) using the unique methods previously described herein.
The methods include exposing and developing the data layer down to the
master substrate. A first generation stamper is made from the master disk
(134). A replica disk may be made from the first generation stamper
(136).

[0077]Alternatively, a second generation stamper is made from the first
generation stamper (138). A replica disk is made from the second
generation stamper (140). Further, a third generation stamper can be made
from the second generation stamper (142). A replica disk can be made from
the third generation stamper (144).

[0078]Photosensitive materials include photopolymers or photoresist, or
other materials or material blends having similar photosensitive
characteristics. One group of suitable photosensitive material includes
standard position type high resolution photoresist commercially available
from vendors Shipley, OCG, etc. Other suitable photosensitive materials
may become apparent to those skilled in the art after reviewing this
disclosure.

[0080]Numerous characteristics and advantages of the invention have been
set forth in the foregoing description. It will be understood, of course,
that this disclosure is, and in many respects, only illustrative. Changes
can be made in details, particularly in matters of shape, size and
arrangement of parts without exceeding the scope of the invention. The
invention scope is defined in the language in which the appended claims
are expressed.